Therapeutic compositions containing nitrate esters



United States Patent 3,355,356 THERAPEUTIC COMPOSITIONS CONTAINING NITRATE ESTERS Robert H. Broh-Kahn, Hastings on Hudson, and Alexander Galat, Yonkers, N.Y., assignors to Bard'Pharmaceuticals Inc., a corporation of New York No Drawing. Original application Apr. 26, 1962, Ser. No. 190,233, now Patent No. 3,275,642, dated Sept. 27, 1966. Divided and this application Sept. 13, 1965, Ser. No. 496,218

4 Claims. (Cl. 167-65) This application is a division of Serial No. 190,233, filed April 26, 1962, now US. Patent 3,275,642, granted September 27, 1966.

This invention is concerned with a new and novel heterocyclic nitrate ester and its water-soluble, pharmaceutically acceptable salts, the method for their preparation and their use as pharmaceutical compounds. In particular, it is concerned with the nitrate ester of 3-pyridine carbinol and its water-soluble, pharmaceutically acceptable salts which are useful in the treatment of coronary artery disease and to produce peripheral blood vessel dilatation.

The organic nitrates are used in therapy to lower the tonus of the arterial wall, thereby relieving arterial spasm. The vasodilatation resulting after the administration of organic nitrates can be demonstrated directly by plethysmographic measurements and by the onset of a blushing phenomenon due to a dilatation of the superficial vessels of the body. While the degree of vasodilatation varies with both the quantity of available nitrate radicals of the particular molecule as well as the organic nucleus, the nitrate compounds have a common site of action which has been established to be directly upon the contractile substance of the blood vessels. It is generally assumed that the organic nitrates act only after being reduced to nitrites; but since excised vessels react promptly to nitrates, they may perhaps act directly as Well. It should be noted in this connection, that the efiective dose of glyceryl trinitrate is onehundredth that of sodium nitrite and on the basis of available nitrite ion, the fatal dose of sodium nitrite for rabbits after intravenous injection is at least twice that of glyceryl trinitrate. Thus, it might be postulated that the organic nitrates act independently although through a similar mechanism as do nitrites or that the reduction of the nitrate group occurs at the site of action.

The most important effect of this class of compounds is the action on the coronary vessels and the peripheral circulation resulting in an increased blood flow. The use of the nitrates in relieving the pain of coronary vasospasm and angina pectoris has been known for almost 100 years. Similarly, the effect of the nitrates in causing vasodilatation of the peripheral arteries has also been firmly established in therapy.

Despite the long term awareness of the beneficial properties of this class of compounds and their widespread usage in therapy, there are many inherent limitations in the use of this class of compounds with the result that of the literally hundreds of thousands of organic nitrate compounds known to chemical literature, only a few have been introduced therapeutically and many of these have been subsequently discarded.

.The principal limitation inherent to this class of compounds is their unpredictable duration of action, the onset of noxious side reactions and the development of a tolerance requiring increasing dosages to maintain the therapeutic efiect. Thus, some of the nitrates act within seconds while others require an hour before an eflfect is observed. The duration of action may vary from a few minutes to more than four hours for a given dosage. These wide diffences-seriously limit the therapeutic application of the individual drugs in that the emergency nature of the at- 3,355,356 Patented Nov. 28, 1967 tack of coronary artery disease does not permit a latent period of an unpredictable nature. Similarly, the marked variation in the duration of action is also a limiting factor.

The seriousness of utilizing a vasodilating compound which has a pronounced effect in dilating the peripheral vessels, without a concomitant effect on the coronary circulation, is readily apparent when we consider the danger of depriving the heart itself of an adequate supply of blood because large amounts of blood are shunted from visceral to peripheral vessels. This shunting of blood from the cardiac to the peripheral circulation represents a serious potential hazard.

In general, nitrate esters may be divided into two therapeutic classifiactions which are based upon their duration of activity. The first group are rapid-acting series and consist of compounds which are easily absorbed, as for example, glyceryl trinitrate, amyl nitriteand sodium nitrite. These agents are of value in providing prompt relief from the excruciating pain of the acute attack of angina pectoris, However, these agents generally exert their effect for such short periods of time that they are of little or no value in the prevention of the anginal attack. The second group consists of the relatively insoluble nitrate esters which are not readily absorbed from the gastrointestinal tract. These agents have a long latent period for the onset of their therapeutic effect. Their slower absorption accounts for their more prolonged duration of action. Such drugs as mannitol hexanitrate, erythritol tetranitrate and pentaerythritol tetranitrate are examples of this class of nitrate esters.

A fundamental limitation of the nitrate group as a whole is their tendency to produce a dilatation of the meningeal vessels, resulting in headaches. These headaches, which last for an indeterminate period of time, may be so distressing to the patient that the administration of the drug may have to be halted. The headache produced by these compounds is primarily due to meningeal congestion which has been confirmed by direct microscopic observation. The brain volume was also observed to increase in man, as did the pressure of the cerebrospinal fluid.

Gastrointestinal distress has also been observed as a side reaction to the administration of nitrates primarily as a result of the hydrolysis of the esters with consequent liberation of nitric acid and also as a result of the direct action of the nitrate ester on the gastrointestinal tract.

Varying degrees of nervousness and anxiety have been observed in some patients after the administration of nitrates, as well as edema, excessive sweating and visual disturbances. H

A tolerance to the action of a therapeutic dose of the nitrates develops on the continued administration of vir tually all of the older preparations. This tolerance requires either that the drug be withdrawn for a period of time or that increasingly larger doses be utilized. Since many of the conventional nitrates are utilized at the near toxic level, further increase in the dosage is not feasible, and, consequently, there is denied the therapeutic benefit of the drug.

Thus, it has been a goal of therapeutic're'search to de-' velop a nitrate compound which would be rapidly absorbed, preferably by either the sublingual or-the oral route and would have a minimal period of onset of action as well as possessing a sustained therapeuticetfect. Such a drug might be used to provide a prompt relief of the acute anginal episode and for prophylactic therapy as well.

In contrast to the properties of the older members of this class of compounds, the nitrate ester of S-pyridine carbinol and its water-soluble, pharmaceutically acceptable salts are readily absorbed by either the sublingual or;

'orah'outes of administration and exert their effect prompttions-and cause a prompt'increase in arterial blood flow.

I'In the preparation of the 3-pyridine carbino'l nitrate ester it is preferred to "first form a salt-of S- yridinecarbin'ol, for example the nitrate, and then proceed with the formationof the nitrate ester. The advantage of this proccdure is the following: since the formation of the ester takes place in the presence of concentrated nitric, which is 'a strong oxidizing agent, there is gerat danger of oxidizin'g the alcohol v:group of the 3-pyridyl carbinol to an aldehyde oFanacidQThis undesirable reaction which can proceed concurrently with the ester formation or might, if properprecautions-are not taken, even completely supercedeit, obviously'can greatly afiect'the' yield'and the purity er the 'des'ired'esterilno'rder to obviate it, it is 'ne'cessary to keep the temperature below 20 and preferably in the range of-' -"5. The reaction of salt formation between 3- pyridine carb nol and'nitric acid, or any other strong acid, is a liighlyexothe'rmic reaction which tends to keep the temperature 'up'if the "3-pyridine'carbinol base is added directly to the nitrating mixture containing concentrated nitric acidand would, furthermore,tend to dilute the nitric acidywh'ich'is undesirable. "By forming the salt first, as a separate 'step, andthen subjecting it to the ester formation this strongly exothermicrphase is eliminated and the formation df'the'ester'canproceed readily'and'in good yield. Howevenit'mustbe noted, that while this procedure ofiers thea'dvantage of "great convenience, the two s'teps,'i.e. the salt formation "and the *esterifica'tion "may be combined. In this case, however, strong agitation and cooling must be used.

While'anyof the halogen "acid salts may be'utili'zed, the nitrate salt is preferred and this salt of 3- yr'idine 'c'arbinol is easily formed by the direct interaction of nitric-acid anu'the pyridine compound, in water. This resultant salt is nitrated'to 'form the ester through the use of concentrated nitric acid in acetic anhydride. While acetic anhydride is a preferred adjunct to the nitration process, aliphatic acid anhydridessuch as propionic'acid'anhydride and'b'utyric acid anhydride may be 'used also. This may be purified to chemical purity thru the use ofpailed solvent crystallization procedures.

The nitrate salt "of the nitrate ester 'of '3-pyr'idine carbinol may also be obtained from the reaction between a 3halorne'thylpyridine 'hydr'ohalide and silver nitrate in an inert solvent, such as an 'alkanol containing from one to five carbon atoms or water. The nitrate salt of the nitrate ester of 3-pyri'dine carbino'l'stays in solution after the'insoluble silver halide is removed by filtration. When this procedure is followed, two mols of silver nitrate per 'mol of hydrohalide salt are used, and water is the preferred solvent. The nitrate salt of the nitrate ester of B-pyridine carbinol is obtained and isolated from the aqueous "solutionby fractional precipitation.

The nitrate salt of the nitrate ester or 'B-pyridine carbinol, is a white crystalline "compound with a melting point of 1 12 C. to 114 C. It is freely solublein'water, resultinginLa clear, colorless solution with an acid feaCtionQThe compound analyzes "for elemental nitrogen in good agreement with the theoretical values, as for example, theory: percent nitrogen, 193; found; percent nitrogen, 19:0.

The nitrate salt of the nitrate ester of '3 pyridine 'carbinol is used to pertuse aniso'lated heart-lung preparation travenously to mice and 800 rug/kg. when administered orally 'to mice. The ratio between the intravenous LD and the oral H1 indica'tes'that the compound is virtually completely absorbed when administered by mouth. The ability of the compound to traverse the gastrointestinal system so that it is readily absorbed and thereby causes an elevated 'bloodlevel, permits a more predictable effect as'well as "a more prompt therapeutic action.

When a solution of the nitrate ester of 3-pyridine car- 4 binol is used to perfect an isolated heart-lung preparation in the dog, utilizing a heart-lung machine and a complete by-pass system, it causes pronounced coronary vasodilatation, the blood flow data with respect to a series taken, being tested shown in TableI.

When this compound is administered intravenously to an anesthetized dog at a dosage level of 10'.0 mgrn/kg, the mean blood pressure drops (within 10 seconds) from 140 mm. Hg. to 63 mm.iHg. At the end of minute'sthe mean blood pressure is 118 mm. Hg,although the'cardiac rate does not then return to the pretreatment level. The blood'pressure and the cardiac rate return to the pretreatment level approximately two hours after the administration of the compound. Evidence of vasodilatation is seen in the increased corneal vascularization which followed the administration ofthe compound and persisted during the period of pharmacologic response.

In the conscious dog, the duration of -ac'tivity -isapproximately 75 minutes-and the blood'pre'ssure decreases from 185 mm. Hg to 93 mm. fHg-a'n'd stabilizes at an average of 125 mm. Hg. In contrast'to this, nitroglycerin produces a drop in blood pressure of approximately 30 mm. 'Hg for a duration of only 4'to '5 minutes.

11' he administration of the compound by the sublingual route to an anesthetized dog results in a marked vasodila- TABLE I [The effect of the nitrate salt of 3-pyridiue carbinol-nitrate on coronar blood flow in the dog] The Nitrate Salt di3 Pyr-idine Control Blood Carbinol Nitrate Body Flow (without Temperature, F. drugs), cc./min.

. Total Dose, Coronary Blood rng. Flow, ccJmin.

83 20 ans 72 20 v88 1 W'eightzlfi kg; Weight of heart (wet basis) gmafConstant extracorp'oreal'blood How from Sigma motor pump required to maintain dog's blood pressure at-start and throughout experimentaSOO ctr/min.

2 Weight: 16 kg; Weight of heart (wet basis) :'110'gm.: Constant extracorporeal blood flow from Sigma motor pumpreq'uiretl to maintain blood pressure atstart and throughout experiment 425 era/min.

Weight: 16 kg.:'Weight of heart (wet 'basis): 110 gm.: Gonstant'extracorporeal blood flow from Sigrnamotor pump required to'rnaintainblood pressure at start andthroughout experiment: 425-cc./min.

To a mixture of '10 m1. of 67 to '69 percent (concentration by weight) nitric acid and '10 ml. of water, is slowly added, with stirring, 5.45 vgm. of'3rpyridine carbinol. The resulting solution is evaporated to dryness'under vacuum (below 1.5 mg. Hg) on a waterbath. The residue isLstirred with ether to crystallize and the crystals are filtered, washed in ether and dried under vacuum. These crystals consist of the nitrate salt of 3 pyridine carbinol, which melts at 106 to 107 C.'The'nitrate salt of S-pyridine. carbinol may be further purified, if desired, by dissolving in boiling isopropanol. Upon cooling, it crystallizes.

12.4 ml. of 90 percent (concentration by weight) nitric acid was added slowly With stirring to .41 ml. of acetic anhydride at 5 to 10 C. To this mixture was added, at

about to C., gm. of the nitrate salt of 3-pyridine carbinol (obtained above). The resulting solution of reagents is maintained at a temperature of not more than 20 C. and, preferably, from 0 to 5 C. for approximately three hours and then an equal volume of benzene is added which is followed by an excess of hexane. Alternately, aromatic solvents such as benzene, toluene, xylene, alkyl naphthalene and alkyl benzene (wherein the alkyl moiety has from 1 to 6 carbon atoms) may be employed, andin lieu of hexane, there 'may be used such aliphatic solvents as pentane, heptane, octane and nonane.

The mixture forms two layers. The upper layer is separated and discarded, while the remaining lower layer is again treated with benzene and hexane as described above. After the separation of the layers, the lower layer is again separated and mixed withan equal volume of benzene and the whole brought into homogeneous solution by the addition of isopropanol. The solution is cooled in an ice chest and allowed to crystallize. The separated crystals are filtered, washed with benzene and dried.

The resulting compound is the nitrate salt of the nitrate ester of 3-pyridine carbinol or the nitrate salt of B-pyridine carbinol nitrate and is a white crystalline compound, melting at 112 to 114 C. The crystals are freely soluble in water to provide a clear, colorless solution with an acid reaction. When tested for nitrogen content by the micro- Dumas method, it was found to contain 19.0 percent of nitrogen, which is in good agreement with the theoretical calculated value of 19.3 percent nitrogen. A mixed melt ing point of the nitrate salt of 3-pyridine carbinol and the nitrate salt of the nitrate ester of 3-pyridine carbinol establishes that the two chemicals are difierent compounds, since the melting point of the mixture of these substances is 80 to 85" C. Furthermore, the addition of ammonia to an aqueous solution of the nitrate salt of the nitrate ester of 3-pyridine carbinol causes the separation of a water insoluble oil which is the nitrate ester of 3-pyridine carbinol. In contrast to this, the nitrate salt of 3-pyridine carbinol does not yield a water insoluble oil upon treatment with ammonia water.

The structure of the nitrate solt of 3-pyridine carbinol imo.

Example 2 To produce a 3-pyridine carbinol nitrate, alkali is added (as for example, potassium hydroxide) to aqueous solutions of the nitrate salt of the nitrate ester of 3-pyridine carbinol nitrate. The oil is extracted with an inert, immiscible, volatile solvent such as ether, benzene, chloroform, hexane, benzin, toluene, alkyl benzene, xylene, alkyl naphthalene, heptane and octane (wherein alkyl refers to alkyl moieties having from 1 to 6 carbon atoms), the solvent evaporated and the isolated oil recovered. After the proof of structure, this may be further hydrolyzed by alkali to 3-pyridine carbinol. A determination of the neutralization equivalent, arrived at in this manner, indicates that 21.8 mg. of the nitrate salt of the nitrate ester of 3-pyridine carbinol is equivalent to 1 ml. of 0.05 N KOH. The theoretical quantity of this ester salt, equivalent to 1 ml. of 0.5 N KOH, is calculated to be 21.6 mg.

Example 3 A solution of 0.652 gm. (0.004 mol) of 3-chlormethylpyridine hydrochloride in 5 ml. ethanol is added dropwise to a solution of 1.353 gm. (0.008 mol) of silver nitrate in 20 m1. ethanol and 3 ml. Water. The silver nitrate solution is warmed on the steam bath during the addition. After the solution is completed the reaction mixture is heated for one more hour on the steam bath to digest the precipitate of silver chloride. The precipitate is re moved by filtration, and on standing at {room' tempera ture, the filtrate yields an'additional precipitate of silver chloride which is removed by filtration. The filtrate is evaporated to dryness and the residue recrystallized from isopropanol. The product'melted at 112 to 114 C.

Example 4 In place of the ethanol used in Example 1 above, there may be substituted any member of the group of alkanols of from 1 through 6 carbons, water or mixtures of these and the remainder of the steps being the same.

Example 6 When it is desired to utilize, therapeutically, the nitrate salt of the nitrate ester of 3-pyridine carbinol nitrate, it may be administered in the form of tablets or capsules. The range in concentration of the active substance (the nitrate salt of S-pyridine carbinol nitrate) is from 1 mg. to 200 mg., administered from one to six times daily, depending upon the status of the patient and the degree of disease present.

To prepare tablets of the nitrate salt of the nitrate ester of 3-pyridine carbinol, the appropriate quantity of the compound is mixed with a diluent or carrier, such as milk sugar, sucrose, corn starch, potato starch or mannitol. The ratio of active compound to diluent ranges from equal parts of active compound and diluent to one part active compound and 99 parts of diluent. The exact proportions to be used in any particular formation depends upon the concentration of active substance desired in the final formulation. To the mixture of the active substance-diluent is then added 0.05 part of a lubricant such as magnesium stearate or vegetable fats (a brand of which is known to the trade as Sterex) and the whole wetted with a solution of 5 percent gelatin-water or 0.05 percent tragacanth-water or 20 percent alcohol-water, and the damp mass passed through a No. 16 mesh screen and dried. To the dried material is then added an equal part of corn starch and 0.05 part of the same lubricant and the whole passed through a No. 40 to a No. 60 mesh screen and then tableted in the selected size and shape.

While the unit dosage range of the active ingredient per tablet is from 1 to 200 mg., a preferred range will be found to be between 5 and 100 mg. per tablet, administered one to six times daily.

It may be desired to administer this compound in a capsule dosage form in which case the mixture of the active ingredient, diluent and lubricant is granulated with a solution of 5 percent gelatin-water or 0.05 percent tragacanth-water or 20 percent alcohol-water, and the damp mass passed through a No. 40 to a No. 60 mesh screen and dried. The dried material may be filled directly into capsules of suitable size so that each capsule contains between 1 to 200 mg. of the nitrate salt of the nitrate ester of 3-pyridine carbinol, and a preferred range will be found to be between 25 and 100 mg. per capsule, which is to be administered one to six times daily.

Example 7 When it is desired to cause a vasodilatation of the arteries and arterioles, as well as in the capillary bed, the nitrate salt of the nitrate ester of 3-pyridine carbinol is administered in unit dosage form as a tablet or capsule, each containing from 1 to 200 mg. of the nitrate salt of 3-pyridine carbinol nitrate, per tablet or capsule. A

prompt vasodilating :eflfect will be observed and an increase in both segmental-and digital blood flow may be ascertained by either plethys-rnographic or oscillometric Example 8 When it is desired to relieve the symptoms of coronary vasospasm and to augment the reduced peripheral blood flow oftheextremities, as would'be present'in Bu'ergers disease, or Ra'ynauds Phenomenon, intermittent claudication and peripheral vasospasm, then tablets or capsules of the nitrate salt'of *the nitrate ester of 3-pyr'idi'ne car binol, each containing from-110 200 mg. of the said compound, may beadministered, from oneto .six times daily, dependent on the needs. :Inthe treatment of such diseases with this compound, 'thedrug may be administered for as long as ;is-necessa'ry. 7

It is not desired tobe limited except as set'to'rth in the following claims, the above illustration of the invention. What -is claimed is:

1. .A therapeutic composition comprising .an effective; amount of the nitrate saltof .the nitrate ester of S-pyridine carbinol and a pharmaceutically acceptable carrier.

2. A therapeutic composition comprising an eflective amount of the nitrate ester of 31pyridine car-binol "and a pharmaceutically acceptable carrier.

3. A therapeutic composition comprising .a compound selected from the group consisting of the nitrate saltof the nitrate ester of 3-pyridine carbinol and :the .nitrate ester of 3-pyridine carbinol and a pharmaceutically ae-- ceptable carrier in unit dosage form so thateach-unit dose:

contains from 1 to 200 mg. of said compound.

4. A therapeutic composition comprising a lpharmacew tically acceptable carrier in .unit dosage form and from 1 to 200 mg. of the nitrate .salt of' the nitrate ester-of "3- pyridine carbinol.

References Cited UNITED STATES PATENTS ALBERT T. MEYERS, Primary Examiner.

SAM ROSEN, :Ex'aminer.

S. J. FRIEDMAN, Assistant Examiner.

description being by way of 

3. A THERAPEUTIC COMPOSITION COMPRISING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE NITRATE SALT OF THE NITRATE ESTER OF 3-PYRIDINE CARBINOL AND THE NITRATE ESTER OF 3-PYRIDINE CARBINOL AND A PHARMACEUTICALLY ACCEPTABLE CARRIER IN UNIT DOSAGE FORM SO THAT EACH UNIT DOES CONTAIN FROM 1 TO 200 MG. OF SAID COMPOUND. 